We are perfusing the left lower lobes of canine lungs with steady and pulsatile flows of autologous blood. By measuring perfusion pressures at different flow rates, airway pressures and states of oxygenation, we seek to learn about the vascular changes occurring with hypoxia, lung collapse, and pulmonary edema. We are stimulating the sympathetic nervous system in these experiments, to learn its role in mediating changes in the pulmonary vasculature. The overall goal of these studies is to learn about systemically-mediated effects in the pulmonary circulation which interfere with the diversion of blood flow from acutely atelectatic or hypoxic lobes of the lung.